The objectives of this study are (1) the documentation of superiority of, and (2) the perfection of techniques for the preparation and storage of human tissue valves used for routine cardiac replacement. The aortic valve homograft is a unitized, semilunar graft obtained from the aortic position of the donor. By specialized techniques of preparation, sterilization and storage, these grafts can then be used for aortic, mitral or tricuspid replacement. Morphologic studies indicate that if the fresh aortic homograft is used within several days of procurement, donor valve cells persist. Such a graft is a living tissue transplant which can potentially function for an indefinite period. Experiments are being conducted in animal implantation and in vitro tissue culture of these grafts in an effort to evaluate their function and ultimate fate. Other experiments are being conducted to optimize techniques for sterilizing (with antibiotics) and storing (by freezing to -196 degrees C) these valves while maintaining their viability, and for mitigating chronic, atypical rejection of these valves by immunosuppressive therapy. We are simultaneously conducting a prospective randomized study which compares the best available prostheses with fresh, viable aortic homografts implanted in the aortic and mitral positions.